Stereo-B is back! Nasa finally reconnects with its long-lost spacecraft

For almost two years, a Nasa spacecraft has been lost and out of contact after passing behind the Sun – but last night the space agency announced it has finally been able to reconnect.

The Solar Terrestrial Relations Observatory (Stereo) B spacecraft, first launched along with sibling A-craft in 2006, has been out of contact since its 2014 orbit around the far side of the Sun.

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As it looped behind the giant ball of hydrogen in October 2014, Stereo-B's communications with Earth were lost. Nasa staff were testing the craft's ability to hard reset – for the possibility that it didn't communicate with the Earth for 72 hours – when it passed behind the Sun and lost a line of sight.

Since the loss of connection the space agency's staff have been working to reconnect with the missing object.

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Most recently, the staff have been using the Deep Space Network (DSN) to try to break the silence. Attempts have been made every month, Nasa says.

"The DSN established a lock on the Stereo-B downlink carrier at August 21 at 6:27 pm EDT," Nasa said in a statement.

"The downlink signal was monitored by the Mission Operations team over several hours to characterise the attitude of the spacecraft and then transmitter high voltage was powered down to save battery power".

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Throughout the entire time Stereo-B – named B, as it is behind the first craft – has been missing in action, its counterpart has been working normally. Nasa launched the duo as part of its Solar Terrestrial Probes program to observe the Sun and Earth.

"Stereo has revealed the 3D structure of coronal mass ejections; violent eruptions of matter from the sun that can disrupt satellites and power grids, and help us understand why they happen," Nasa says.